The question involves an OSPF router receiving both an E1 (External Type 1) and an E2 (External Type 2) advertisement for an external network with the same path cost. The task is to determine which path the router will prefer.

Analysis of Options:

Option A (ECMP):Equal-Cost Multi-Path (ECMP) is used when multiple paths have the same total cost, but E1 and E2 routes have different metric calculations, so ECMP does not apply here.

Option B (Prefer E2):Incorrect, as E2 routes are preferred only when E1 routes are not present or have a higher total cost.

Option C (Suppressed):OSPF does not suppress routes due to path conflicts; it selects the best path based on metrics.

Option D (Prefer E1):Correct. OSPF prefers E1 routes over E2 routes because E1 routes include the internal cost to the ASBR (Autonomous System Boundary Router) plus the external cost, providing a more accurate total cost.

Why Option D is Correct:In OSPF, external routes are advertised as E1 or E2. E1 routes include both the external cost (advertised by the ASBR) and the internal cost to reach the ASBR, making them more precise for path selection. E2 routes only consider the external cost and are the default for redistributed routes unless explicitly configured as E1. When an OSPF router receives both E1 and E2 routes with the same external cost, it prefers the E1 route because it accounts for the total path cost, including internal network topology. This is per OSPF standards (RFC 2328).

Relevance to Certification Objectives:

Routing (16%):Involves designing and troubleshooting OSPF routing topologies, including external route types (E1 vs. E2).

Troubleshooting (10%):Includes analyzing OSPF path selection to resolve routing issues.